Magnetic compass



y 1945- BIE. SHERRILL 2,375,329

I MAGNETIC COMPASS Filed May 20, 1945 4 sheets-sheet 1 -Ju'vl I}. 5126:2122

INVENTOR.

-///5 Jrramx May 8, 1945. B. E. SHERRILL MAGNETIC COMPASS Filed May 20, 1943 4 Sheets-Sheet 2 38% 88 gm 1?. sw g-l ymfizfly B. E. S HERRILL MAGNETIC COMPASS Filed May20, 1945 4 Sheets-Sheet 3 Willllllll fizwlll S/zenz'll ///5 lira/Quay y 1945- B. E. SHERRILL 2,375,329

MAGNET IC COMPAS S Filed May 20, 1943 4 Sheets-Sheet 4 llllllllllll'v Jud/ l Sfiezrll/ IN V EN TOR.

Patented May 8, 1945 9 c r V UNITED STATES. PATENT OFFICE.

MAGNETIQCOMPASS Burl E. Sheri-ill, Peru, Ina-f 1 a Application May 20, 1943, Serial. No. 431,721 i '8 Claims. (Cl. s3.-.-2.25)

This invention relates to a magnetic compass and more particularly to improvements in a magnetic compass having as'i'ts principal'object Sim-- ple construction, facile assembly and economical manufacture.

Another object of this inventionis to provide a composite compensator arrangement for a magnetic compass whereby'to overcome the distracting effect of magnetically attractable objects and stabilize the magnetic compass relative to the "particular vehicle with which itis associated.

Yet another object of my invention is to provide a compass rose rotatively movable in a fluid filled bowl with fractional buoyancy'to increase the sensitivity of the responsive qualities of the:

magnetic bars it carries. v

Still another object of my invention is to provide' a movable compass bowl encasing' a floating compass rose and alubber line associated therewith in a manner to overcome a constant-error in the compass relative to the casing.

A further object of this invention is to provide a simple, yet effective, means for afie'ctingaheel- 'ing compensation formagnetic compasses.

A still further object-ofthis invention is to provide a compact and interrelated arrangement of parts for accomplishing both preliminary and Other objects will appear more-fully hereinafter.

The invention consists in'the novelcombinationand arrangement of parts described and claimed. I

- The invention will be best understood by reference to the accompanying drawings showing my new compass arrangement, andin-which." Fig. 1 is a perspective view of my preferred form of compass structure; a Fig. 2 is an exploded perspective view of the head assembly; I A

Fig. 3 is a bottom plan View of a part employed in the head assembly as seen from'line 3-3 in Fig.2;

Fig. 4 is an exploded perspective view of the compensator assembly; I

Fig. '5 is a bottom plan view of a Patti of the compensator as seeniirom'below in Fig. 1 from line 5-5thereof;

to be hereinafter in Fig.1;

i 'Fig. 6 is a side elevational' view of an index ring associated with the compensator assembly;

Fig. 7 a vertical sectional detail through my compass structure as seen looking in the direction of line T- -T in Fig. 1; V

Fig. 8 is a vertical sectionaldetail through the compass structure 1 as Fig.'7;- 1 i Fig. 9 is a persp c'ti'vediagram illustrating the principle employed in the compensator assembly;

Fig.10 is a bottom plan vie-w of a magnet carrier employed in the compensator assembly;

l 'igril is a horizontal-sectional detail through my compass structure asseen from line H,H

Fig. 12--is a bottom plan-view of the compass rose seeninFi'g, 11;"

Fig, 13 is a. horizontalsectional detailthrough the lower portion of my compassstructure substantially'along-line' l3--l'3 in Fig. 7 and showmg the quadrantaladjusting and compensating arrangement;

ig.'14' is a perspectiv'e'view of the underside of a compass case showing a modified form of quad'rantal adjusting and compensating arrangement'; Fig. 15 is aperspective view of a modified form of compass case partly disassembled anddisclosing a-modified form of compensator assembly;

Fig. 16 is a horizontal'sectional detail through 'the'niodified compensator assembly as seen along line [S -16in Fig. 15;

Fig. 17 is a fragmentary vertical sectional detail view as seen from line l-l--l1 in Fig. 16; and Fig. 18 is a horizontal sectional detail view taken through certain drawer arrangement formmg a part of my modified form of compensator assembly as seen substantially from line l8-l8 in Fig. 1-7;

This invention contemplates the provisio'iiof a magnetic compass 'for'use in the most rugged types of vehicles where the possibility of disturbing factors-are extremelygreat. The conditions and surrounding circumstances which prevail in tanks employed in warfare have the most dis- '-tracting effects-on magnetic compasses and it is with these affects in mind that the present invention has been conceived. I

main section 3 is'provided with a pair of axially alignedbearings 6 horizontallydisposedand providing a swinging support adapted to receive seen from line- 8-1-8 in to embrace the skirting of the dome.

mounting 'bolts I at the sides of the main section which mounting bolts are in turn carried 'by a suitable mounting bracket 8 shown in part in Fi 8.

' The main section compass card when the housing is jarred. In addition to this feature I have provided an air tight chamber 24 in the compass rose which chamber may have its air evacuated to form a vacuum therein. By reasonof this construction the normal weight of the body 2| is decreased and made of a transparent materialsuch as a heavy,

an open end adapted to be closed by a baflle plate l6 which rests on 'a' shoulder l1 formed ontheainside face of the cup l4 a substantial distancebelow the upper edge of the cup l4. A compass rose I Sisdisposed within the bowl l3 for rotative movement relative thereto on a bearing post I 9 suitably supported on the bottom wall l5and having arecessedvupper end l9 adapted to receive,-and support a needle extending downwardly from the rose l8. ,The-compass rose l8 consists of-a plastic body 2|v having a dome shaped center 22 with two parallel grooves23 formed on the sides thereof A pair of bar magnets '38 are pressed into the respective grooves 23 to render the compass rose sensitive to'the influences of the earths magneticjforce. Thebalance of thebody is'rec'essed on its upper surface surrounding the dome, 22 to form an open v topped chamb r 24 adapted-to receive a segment of a sphere 25 to seal the chamber 24 relative to the interior ofgthe bowl l3 for reasons presently" It has a central detent 24 which lies closely adjacent the upper surface of theseg! ment 25 in such a manneras to retain the point 0f the needle 20 within .the recess l9"to prevent displacement of the compass rose therefrom. As willabe seen in; Figs. 8 .and 11 the baffle plate [6 has a plurality of spaced apertures 28 which perthermal plastic and having a bottom .wall [5 and a the buoyancy of the compass rose increased in order to lighten the load of. the compassrosevon the point of the needle 20 thereby increasing the sensitivity of the compass reactions under the influence of polar fields. e I

' The cylindrical body 9 has an opening 39 iormedin the, front face thereof through which opening 39 the bowl and compass rose may be viewed. The rearwall of the body 9 has a horizontal slot 49 formed therein through which extends a shank 4| of a knob '42 which is attached to the'bowl I3 to provide a handle for the .bowl

whereby to facilitate manual rotation of the bowl 13 relative to the chamber ID in the body 9.

I Under normal conditions the lubber line 30 is mit passage of fluid from thebowl l3to the upper 1 opening thereof whichin turn is sealed by a re-j silientdiaphragm 29. l

The compass bowl l3 also provided with a lubber line 30 which is in the form of a piece of thin non-ferrous .material having a base 3| adapted to be pressed into a slit 3-2rormed on the inside face of the bottom wall l5 and having an upstanding portion 33, arcuate in shape, to permit tiltability of the compass rose I8 and pro vide, a fixed indicator line with, respect to the rhumb points on thecompass card 36.

v The bowl I3 is filled with a suitable-liquid 34 through an opening 35 formed in the bottom wall 15- and suitably sealed thereafter by a plug 31.

[The liquid 34 is intended to completely fill the cup l4, however, there is always a possibility of:

air bubbles forming in thebowl and for this reason the space between the baffle plate l6 and the,

.diaphragm 29 is provided to impound such air;

bubbles above theactual compass bowl, :As is well known the liquid 34 stabilizes the 'of the body 9 by a pair of set screws 44 which pass through a horizontal slot 45 formed in the plate43. i v

V The head assembly The compass I is provided with, a compensator unit for overcoming deviations in readings onthe compass relative to the magnetic compass directions. This compensator unit housed in the head section 4 which is enclosed by is completely asplit .bodyportion 46118101 in position on the body 9 of the main section 3 by a screw cap 41 which is threadably connected to an upstanding post 48 forming a portion of the compensator now to beexplained. a

There are three principal phases of compensation accomplished by means -confined in the head assembly of the compass structure, the first being a rough or preliminary semicircular correction hereinafter referred to as freeing; the second 'being a fine or Vernier semicircular adjustment of certain supplemental bar magnets for the purpose of attaining as near a correct reading asis possible; and'the third beinga correction to overcome vertical magnetic influences which third form of correction, is commonly called heeling. 3 I v l 1 7 Turning now to the drawings, particularly Figs.

at 5|. The freeing compensator 49 is well illustrated inrFigs. 4 through 6 inclusiveconsidered :medial plate 54.

in View of Figs. 7 and 8-, and as seen in the'views referred to it is an object of my improved construction to dispose the compensating barmagnets in as closely spaced arrangement as is physically possible. vide a dual purpose unit 49 wherein both north and south compensation and east-west compensation are confined to a relatively small vertical space with a minimum number of working parts. a The compensator 49 consists of a pair of index rings 52 and 53 spaced from each other by a I The ring 52 indicates northsouth adjustment and is suitably positioned on a reduced portion 55 of an upper plate 56 while the ring 53 indicates east-West adjustment and surrounds a reduced portionr51 on theemedial plate 54 and lies on top of the peripheralflange ofa dividing plate 58. The freeing compensation is in effect a semicircular compensation butisa In accomplishing this end, I propreliminary form of such semicircular compensation, and for this reason the freeing and semicircular compensators #9- and respectively are structurally similar. Thus it-will be seen that like-parts are present in each ofthese units such asa pair of rings 52 and 53 spaced from each other by a medial plate 54', the ri ng'fil surrounding 'a reducedportion 55' on the diVid-Z ing plate 58 whilethe ring -3" surroundsthe reduced portion 5 1 on the medial plate 54'. The lowermost ring 53" rests onthe-top H of the casing 9, as does the reduced portion. 51", in such a manner as to'provide sufficient clearance to-- permit free rotation of the ring '53" about the portion51. a a t I The medial plate 54 is recessed as shown Fig. 4 to receive horizontall -disposed mag-net carrying gears'59' meshing with each other and plate and alsohas a gear pinion 62 engageable with the inner gear face of the index-"ring '52 portion 51 to transmit rotative movement to the gears 59 through the" geartll. "A floating gear 63 is suitably journaled in the upp-er' iate 5'5 and at a point relative to the control whe'el'fi'l and the transmission gear 60 as to assurethe disposal of the ring 52 concentrically with respect to the reduced portion 511' As'sen Figs. 4 and 3 all three of these goals, namely the pinion gear 62, the transmission gear 60 andthe floating gear arm alignment withrespect to each Othfflfld so that they can be simultaneously adjusted in equal and oppositeang'ular directions with respect to a plane through the axis oi the compass rose.

': The upper Wa It oi the casing an: the main section has an oval shaped opening H iorme'd therein to receive a portion 12' of a mounting plate 13 which isin'serted'up through the open bottom I2 of the case 9. The portion 12 has'a pair of tangential recesses formed therein to receive the lowermost magnet carrying gears -61 and at diagonal points has bolt holes maligned I with like holes M ineach of the-superimposed plates 5Q, 58, '54- and 56 to'permit mounting screws (not shown) to extend upwardly therethrough for binding relation with the 'flangefi on the upstandingpost 48. e i This upstanding post 48 has a plurality of vartically arranged passages 16 formed therein for the purpose of receiving bar magnets tosupport them vertically above the compass rose in closer proximity to the vertical axis thereof} This structure comprises the heelin-g compensator heretofore mentioned and includes-a series of bar magnets 11 as shown in Figs. '1 and 8- to vary the ,magnetic influence to be appliedyin heeling the magnetic compass.

' whereby to rotate the latter about the reduced compass structure.

63 are disposed in a respective recess formed in the reduced portion 55 of theupp'erplate 56 similar recesses being formed in substantially similar locations on the reduced portion '51 of the medial plate 54 as shownin Fig.5.

The ring 53 is disposed on the reduced shoulder 51 and has its inner gear face in mesh with the pinion 64 of a control'*wheel'6-5 also disposed in the medial plate 54. The inner gear face of: the

ring 53- in turn meshes with a transmission gear 66 to transmit rotative movement into a p'air. of

magnet carrying gears 51' similar to the gears .59 but disposed at right "angles-with respect thereto. These gears 61 and the pinion tgear thereof are lodged in'a' recess'formediir'r the top surface of the dividing plate 58 and similar in relation with respect toeach other as is the case of the recesses formed in the upper "face of the medial plate 54. Thus thefreeing unit 69-has both a north-south adjustment and an east-west adjustment in a minimum vertical heighth'. The semi-circular compensator being similar in character like reference numerals withanexponent or prime character thereafter indicate like parts. I

The magnet carrying gears 59, 51, 59; and G1 are constructed as best illustrated in Flglo with l a plurality of parallelly arranged pockets 68 formed in their bottom face with a central pocket 69 arranged along a diametrical axis of the gear and symmetrically spaced pockets on the sides thereof. These pockets are adapted to receive magnetic bars 10 in quantities, the number being determined by the particular distracting magnetic force of induction tobeove'rcome As shown in Fig: 9 these pockets i8 are-{so formed as to dispose the magnetic bars" 10- in "perfect points on the compass. I to the shaft 18 in order to maintain the various Having thus described my improved arrange- 'ment'for compensating b permanent magnetism I-now refer to the lower portion 5 of my new Lower portion Quad-Tania; I I I As hereinbefore explained the open bottom i2 of the casing 9 has a'bottom panel 12' disposed therein to support the bowl [3. This panel: I 2" has its peripheral edges attached to the inner walls of the casing 9 byany suitable method and has depending from its central boss, coaxially with respect to the compass rose, a keyed shaft 8 adapted to support a nonconductive co1lar'19 at various points of adjustmentfrelative to the bottom of the compass bowl; This collar" N carries a plurality of radially extending arms 80, more particularly 1 four, disposed fore, aft, I port and starboard, and-four others at diagonal points,

makingin all eight of such arms. The arms au, being considered in sets of four, are quadrantal correctors', one quadrantal correctorv beingemployed to effect a compass correction to the fourc'ardinal points on thecompassand thefi'other to effect compass correction at mid cardinal The collar 19' is keyed arms at the desired anglesoi radialprojem tion, but may be movedvertical-ly to any desired position relative to the compass'rose.

The arms 80 serve-t support' metal collars' fll in limited numbers as isbest illustrated in Fi-gs 18.

known in the art as Permalloy which has a rel- 1 3 low capacity as to the retention ma net/ismh y permeable with hysteresis curve accordingly); These'collars 81 serve as compass correctors' by neutralizing the effects Y of the vehicles magnetism. Each of the arms 9|] are threaded and receive a nut 82 for the purpose of securing collars 81 in series in fixed position on the-arms. 1' INT, The quadrantal compass correctorisenclosed by a cover '83 having an opening formed in its bottom wall 84 to permit the threaded end 85of the shaft 18 to extend therethrough for the recep- '75 t-ionof'a knob at. A friction disc 81 is disposed 2375329 I betweenjthe knob 86 and the'bottom Wall 84 of the 1 cover 83 whereby to secure the latter in place on the casing 9 and yet permit rotative movementof 1 thecover 83 relative to the casing 9. The cover.83 l

in addition to serving as an enclosure for the quadrantals, as hereinbef-ore explained, is-also a 3 course indicator 88 for the compass structure. To

this end-the upper end of the cover 83 has a beveled surface 89 on which is inscribed rhumb lines 1 similar .to those on the compass card 36.

The cover 83 also has anannular projection 90 which serves as a finger engaging surface whereby to manually rotatethe course indicator '88 to a desired angular direction it is desiredthat the vehicle shall travel and hence when the rhumb lines of compass card 36 coincide with those of the. course 1 1 indicator the vehicle will be facing in the desired direction of travel.

Operation the knob, thus bringing thelubber line inper- In use the" compass structure is installed in the vehicle with which it is to be associated, the

bracket 8 being properly bolted on the body of the vehicle. The compass structure is then stripped 1 7' l of all auxiliary metals such as the bar magnets l H in the heeling assembly as well as the perm-v alloy collars on the quadrantalsm The freeing and Vernier magnet carrying gears 59-61-5595 and 61' are positioned in alignment with their re- 1 j'spective bar magnets neutralized with the cor- 3 responding bar magnet on the opposite gear. The

vehicle is then faced due north with motor running and other gear in a normal condition for compass card taken. This is repeatedfor each of traveling'of the vehicle, and the reading on the l the other cardinal points of the compass; By mathematical formula the deviations in reading I j are used to calculate the, amount of compensation 5 points of the compass, the freeing gears 59 and the V control wheels BI and 65 thereof rotated to simultaneously adjust the gears 59-6l to dispose necessary to overcome the error at the various 1 theirrespective magnets min equal and opposite angular directions relative to each respectiveset j of gears.

the general influences of" magnetic bodies within 1 the'vehicle the foregoing procedure is repeated 3 with respect to the vernier semicircular compensator in anefiort to eliminate any error in 3 reading completely.

Having thus freed the magnetic compass from c them in the desired position of adjustment. As will be noted in Fig. 14, the bars 8| are varied The next step is to makea heeling adjustment j which is accomplished by tiltingthe vehicle approximately 10 with respect to the vertical with the compass reading be the same when the vehicle is in tilted and level position'and to this end bar the desired passages 16 until the readings are 1 identical oras close thereto as to permit only of a fractional error.

the vehicle facing due north. It is'desirable that magnets 11 of necessary number are dropped into l ssl am m n sj t he eni e r' ll n e e '55 In this regard feet alignment with the particular directional rhumb line on the card 36. Completin this last adjustment it is essential that the zero indicia on the indexing plate 43 on the front wall of the casing 9- be in perfect alignment with the lubberline 30 and hence it must be shifted. v v

After the compass structure is once installed in a vehicle and tested in the manner hereinbefore set forth, periodical tests must be made to at all times assure a proper reading of the compass.

Suchperiodical tests, however, are not as detailed asan original test, it being necessaryonly to manipulate the control wheels 6| or and 6| or .65'and other minor manipulations of surrounding compensators. V V c Modifications A modified formof .quadrantal compass corrector is. shown in Fig. 14 which illustrates the bottom section of a casing 9 having adepending shaft 18 which has holes drilled across its length to receive bars 8l' of. permalloy material to overcome the influence of surroundingmetallic bodies in the same manner asdo the collars 81. There are two sets of such holes in the shaft 18' consisting of four holes each. These'holes are spaced from each other along the axis of the shaft 18 and are staggeredas seen in Fig. 14 so'as not to interfere {with each other. A rubber collar or other frictional means I9 is mounted on the shaft 18' and hasholes formed therein in alignment with the holes in theshaft l8 and serves to frictionally grip the insertedbars 8 l to maintain in length, they being selected according to the need forgreater or lesser quantities of metal in order to arrive at-the ideal adjustment of the compass rose. It is also pertinent to note that the two vertically disposed sets of holes enable the insertion of bars 8| at varied distances relative to the compass rose. It is also important to note that the bars 8| may extend more to one side than the other of the shaft'l8, thuspreis shownin Figs. 15 through 18 in which like parts have like reference numerals with respect to those used in explaining the preferred form of compass structure.

I In this modified form of construction a cover!!! is provided for the head assembly which cover BI is normally disposed onthe top of the casing .9 and held thereon by atthumb nut 92, andstud screw 93 the latter of which extendsupwardly from the head assembly.

. In this form of compensator the freeing com-,-

pensation is accomplished by drawer type magnet carriers indicated at 94. In thisform of freeing compensator the bar magnets 95 are reduced or ture it is apparent that I have provided a c increased in numb'er'to suit the particular on cumstance and are otherwise 'static reiative to thecompass rose. The "vernier 'ad'justmeritjof' semicircular compensation is accomplishedhy providing "a pair of magnet carrying gears 95' disposed in a plane par-allel toj the fore and aft axis of the vehicle a pair oflike gears =91 disposed crosswise with respect to the aforesaid axis; The "body 98 of the head assembly is made in three sections the lower one 99 having crosswise slots formedtherein, 'one'above the other,

to'receive the "drawers 9!; The r'en 'aini-ng two ried by said platesan 'upstanding'post arranged on said super-imposed platesland' having a plurality of vertically disposed i passages formed The body 98 has vertical grooves in formed thereinat the front and backyas well as at thetwo sides to expose the periphery of thegear sets 96 and '91 whereby theymay be manipulated to swing the bar magnets 95 carried thereby into desired positions of adjustmenti l Having thus described my new compass struc pact unit of relative simple constructions-mploying. a minimum number of working parts. The advantage of this structure over other known types of magnetic compasses is found in-the fact that there are less parts rendering the device easy to assemble and permitting the arrangement of compensator means relatively close to the compass rose and requiring but little additional height in the compass structure.

While I have illustrated and described the preferred form of construction for carrying my invention into eiiect, thisis capable of variation,

l. A compass structure including a casing having a main section and a head assembly, a compass bowl arranged in said main section, a com pass rose arranged in said bowl, alpair of semicircular compensators arranged above said main section and invsaid head assembly and comprising a series of superimposed plates, magnet-carrying gears in mesh for horizontal rotation car-,

ried by said plates, an upstanding post arranged on said superimposed plates and having a plurality of vertically disposed passages formed therein to receive a predetermined number of bar ,magnets calculated to overcome induced magnetism emanating from'the vehicle in which the compass structureis installed, means for securpass rose arranged in said bowl, a pair of semi circular compensators arranged above said main section'and in said head assemblyandcompris ing a series of superimposed plates, magnet-carrying gears in mesh for horizontal rotation cartherein to receive..-a predeterminediiumher of bar magnets'eal-culated to overcome induced mag. netism' emanating from the vehicle in whichthe compass structure is installed, means'iorse'curing said superimposed plates and said upstanding post to said main section, cover means for Ken-'- closing said head assembly, cap means threadab arranged on said upstanding post and securing said covermeans on said main section, arcompass correcto'r on said lower portion and tncliidinga depending shaft, a plurality vof radially lezctending arms adapted to receive ferrous 'ae'lementsrto neutralize the effects of surrounding magnetic bodies, a course indicator for .said compass and f'or' enclosing said compa'ss eorrector, and mealn-s securing said course indicator for rotative moire ment' on. said depending shaft with the rhur-nb lines or said course indicator disposed in close proximity to said compass rose.

3. In a magnetic compass structure including a housing, a compass {ca/rd arranged in said "housing a semicircular compensator comprising, in combination, a pair of gears for supporting "bar magnets diametricallythereof and arranged in the upper wall of the housing for horizontal intermeshing relation, a transmission gear engaging one of said gears, an annular ring having an internal gear face engaging said transmission gear, a plate member having a reduced portion arranged within said annular ring, and control means journaled in said plate member and, having a gearvpinion in mesh with said internal gear face, said control means protruding exteriorly of said plate member for manual operation to rotate said annular ring and said pair of gears to simultaneously adjust bar magnets carried thereby in equal opposite angular directions with respect to said compass card.

4. A semicircular compensator for a magnetic compass andcomprising a head plate having a reduced portion on its lower face, an annular ring arranged to surround said reduced portion and 'having an internal gear face, a medial plate arranged beneathsaid annular ring and having a" recess formed therein, a pair of magnet carrying gears arranged in said recess for rotative movement, means linking said magnet carrying gears with the internal gear face on said annular ring,

an offset recess formed in said medial plate and exposed through the periphery of the latter, con: trol means disposed in the offset recess in said medial plate for manual operation and having a pinion in mesh with said annular ring whereby to facilitate adjustment of said magnet carrying gears relative to the compass structure.

5. Acompensator head assembly for a compass structure including a compass housing having a' horizontal recess formed therein, magnet carrying gears supported in said recess for intermeshing relation, an indexing ring arranged concentrically on said housing, means for transmitting motion from said indexing, ring to said magnet carrying gears, a medial plate arranged on saidindexing ring and having a reduced portion depending therefrom and disposed within said indexing ring to support the latter for concentrical rotation on said housing, and means for simultaneously rotating said indexing ring and said magnet carrying gears.

6. A head assembly for a compass structure including a compass housing, in combination, a

freeing compensator and a vernier compensator,

said compens'ators arranged-in a series of narrow plates superimposed one above the other, each of said compensators including a base plate having tangentially disposed circular recesses formed: therein, a pair of gears supported in said recesses for intermeshing relation and having diametri-I cally disposed pockets formed therein to support magnetically attractable bars, an indexing ring having an internal gear face arranged concentricallyon said base plate, a medial plate arranged on said indexing ring, a spacer plate arranged within said indexing ring to space the:- medial plate from said base plate to permit ro-j tation of said indexing ring, bearing means formed in said base and spacer plates, transmis-L sion means in said bearing means for linking one of said gears with said internal gear face, andcontrol means J'ournaled in said spacer and me'-. dial plates and protruding exteriorly of the pe-" ripheral, edge of said medial plate and having: means linked to said internal gear face for rotat- 'j ing' the indexing ring and pair of gears, said 1 medial plate having tangential circular recesses disposed therein at right angle with respect to the recesses formed in said-base plate, a pair of magnet carrying gears supported in the recesses of the medial plate, a second indexing ring arranged on said medial plate, a headplateforming a base, plate for the upper compensator unit and disposed above said secondindexing ring and having a depending reduced portion disposed within said indexingring, a second control means journaled in said reduced portion and said me-,

adapted to; receive magnetized bars calculated to neutralize the effects of vertical magnetic fields ad acent said compass structure. a I t 8. 'A heeling compensator for a magnetic compassstructure including a housing and a compassrose, a plurality of vertically disposed pock ets formed in said housing above said compass rose in close proximityto the vertical'axis thereof, and a plurality of permanent-magnet bars selected for disposal in said passages for overcoming the influences of vertical magnetic fields created by adjacent bodies in the vehicle with which the compass structure is associated.

BURL E. SHERRILL. 

